Process for the catalytic oxidation of ammonia and methane to hydrogen cyanide

ABSTRACT

A process for the oxidation of ammonia to hydrogen cyanide which comprises combining ammonia with a predetermined amount of oxygen and methane to produce hydrogen cyanide and water and passing the resulting mixture over a ceramic catalyst of the following empirical formula at a temperature between about 700° and 1100° C.: 
     W k  X n  J.sub.(1-k-n) ZO.sub.(3±m&#39;) 
     Wherein: 
     W is zirconium, tin or thorium or mixture thereof; 
     X is an alkaline earth metal or mixture thereof; 
     J is scandium, yttrium, a rare-earth element or mixture thereof; 
     Z is a metal of the first transition series or a mixture thereof, at least 0.01% of said metal having an oxidation state other than +3; 
     k is a number having a value of between 0 and about 0.1; 
     m&#39; is a number having a value of from 0 to about 0.26, provided m&#39; has a value other than 0 when n has a value of 0; and 
     n is a number having a value from 0 to about 0.51, provided when n has a value of 0, k has a value of between 0 and about 0.05. These mixed oxide catalysts can be used to catalytically oxidize organic compounds to various states of oxidation, ammonia, carbon monoxide, hydrogen, sulfur dioxide, and hydrogen sulfide, with oxygen, or carbon monoxide with water, sulfur dioxide or nitric oxide. The catalyst can also be employed in the catalytic removal of carbon monoxide, hydrocarbons, nitric oxides and sulfur dioxide from the exhaust gases of generating or heating plants and automobiles burning fossil fuels. In addition these catalysts can be employed to produce hydrogen cyanide from methane, ammonia and oxygen.

This application is a division of application Ser. No. 556,670, filedMar. 10, 1975, now U.S. Pat. No. 3,976,599, which is a division of Ser.No. 194,769, filed Oct. 8, 1971, now U.S. Pat. No. 3,885,020.

BACKGROUND OF THE INVENTION

This invention is directed to a class of oxidation catalysts, tocatalytic oxidation processes utilizing oxidation catalysts, and tomethods of catalytically treating exhaust gases with oxidation catalyststo produce exhaust gases substantially free of harmful pollutants.

More particularly, the present invention is directed to a class ofceramic, mixed oxide, nonstoichiometric electrically neutral, oxidationcatalysts of the following formula:

    W.sub.k X.sub.n J.sub.(1-k-n) ZO.sub.(3±m')             (I)

wherein

W is Zirconium, Tin or Thorium or mixture thereof;

X is an alkaline earth metal or mixture thereof;

J is scandium, ythrium, a rare-earth element or mixture thereof;

Z is a metal of the first transition series or a mixture thereof, atleast 0.01% of said metal having an oxidation state other than +3;

k is a number having a value of between 0 and about 0.1;

m' is a number having a value of from 0 to about 0.26, provided m' has avalue other than 0 when n has a value of 0; and

n is a number having a value from 0 to about 0.51, provided when n has avalue of 0, k has a value of between 0 and about 0.05.

In addition, the present invention is directed to processes for thecatalytic oxidation of organic compounds to various states of oxidation,ammonia, carbon monoxide, hydrogen, hydrocarbons, sulfur dioxide andhydrogen sulfide with oxygen; of carbon monoxide with water vapor,sulfur dioxide or nitric oxide; and of a gaseous mixture of uncombustedor partially combusted fossil fuel, carbon monoxide, carbon dioxide andatmospheric gases with oxygen without the concomitant production andemission of nitric oxide in the exhaust gas, employing the catalystdescribed herein. Furthermore, the present invention is directed tomethods of treating exhaust gases from chemical plants, electricalutility generating plants, heating plants, steel mills, smelting plants,trucks and automobiles to remove gaseous pollutants, such as carbonmonoxide, hydrocarbons, partially oxidized hydrocarbons, the oxides ofnitrogen, and sulfur dioxide, and hydrogen sulfide therefrom.

Since the advent of modern technology, air pollution has become aserious and tragic problem for man. The present industrial plants andautomobiles which burn the fossil fuels emit a staggering amount ofgaseous pollutants, principally unburned or partially burned fossilfuels, carbon monoxide, the oxides of nitrogen, sulfur dioxide andozone. These pollutants are chemically reactive and have been found tobe harmful to both plant life and animal life. Under certain weatherconditions, the accumulative emissions of these pollutants can havetragic effects. For example, in late 1930 about sixty people died andanother 6,000 became seriously ill from breathing abnormally high levelsof gaseous pollutants in the Muse Ruhr Valley of Belgium. A more recentcalamity took place in the mill town of Donora, Pennsylvania, in 1948.The death smogs or fogs that hovered over London, England, in 1952 and1962 are well documented. As stated above, gaseous pollutants not onlyaffect animal life but they also affect plant life. Smog has been foundto have a serious effect on the evergreen trees growing on the mountainsides surrounding the Los Angeles basin. Furthermore, the University ofCalifornia Air Pollution Research Center has found that smog has adetrimental effect on the growth and the fruit yield of citrus trees.

Smog is a by-product of a complex series of photosynthetic reactionsthat occur in the atmosphere when certain molecular species are foundtherein. More particularly it has been found that the production ofphotochemical smog requires nitrogen oxides such as nitric oxide andnitrogen dioxide, hydrocarbons, and ultra-violet light. One of thepossible routes for the production of smog is theorized as follows:During the combustion of a fossil fuel the oxides of nitrogen areformed. These nitrogen oxides and some unburned fuel together withcarbon monoxide are emitted in the exhaust gases. In the presence ofhydrocarbons and sunlight the nitric oxide is photochemically oxidizedto nitrogen dioxide. The nitrogen dioxide molecule is thenphotochemically split into nitric oxide and atomic oxygen. A portion ofthe atomic oxygen in turn interacts with molecular oxygen to form ozoneor with hydrocarbons to form complex and reactive oxidation products. Itthen appears that a portion of the ozone reacts with the nitric oxide toprovide a fresh supply of nitrogen dioxide. Another portion of theatomic oxygen and a portion of the reactive hydrocarbon oxidationproducts in the air form free radicals which in turn react very readilywith oxygen, nitric oxide, nitrogen dioxide, and with other hydrocarbonsto form more complex materials such as peroxyacyl nitrates. Theperoxyacyl nitrates are suspected of being the principal cause of theeye-searing effect of smog; it has been documented that these compoundscan cause substantial damage to crops when present in exceedingly smallamounts, such as parts per hundred million.

From the time the primary gaseous pollutants known to causephotochemical smog were identified, it has been recognized that theelimination of these gaseous pollutants from the exhaust of industrialplants and vehicles would substantially eliminate photochemical smog.The chemical industry has been working diligently in this field over thelast decade in an effort to accomplish this result. Some of the efforthas resulted in the introduction of devices that give limited results,such as the smog-emission devices introduced on automobiles in the late1960's. Other efforts have been directed toward catalysts and catalyticsystems which can reduce the amount of hydrocarbons, carbon monoxide andnitric oxide emitted from the exhaust gas of motor vehicles andindustrial plants burning fossil fuels. This effort has only beenpartially successful for a variety of reasons. For example, many of thecatalysts developed were prepared from precious metals such as platinumand palladium; the resulting catalysts are relatively expensive. Manycatalysts are readily deactivated by sulfur, oxygenated sulfur compoundsor metals, such as lead. Other catalysts are environmentally and/orchemically sensitive and are rapidly inactivated when operated at hightemperatures or in the presence of certain materials. Many of thepresent catalysts are only effective at low space velocities and canonly be utilized in a catalytic system having a large catalytic bed andcatalytic chamber to provide sufficient contact time between the exhaustgases and the catalyst. The catalytic systems that have been developedare generally quite complex and require more than one catalyst with eachcatalyst operating within a particular temperature range. To ourknowledge no catalytic system has been developed for the removal of themajor gas pollutants from fossil fuel exhaust fumes utilizing onecatalyst which can effectively operate over a broad temperature of theexhaust gases.

An object of the present invention is to provide an oxidation catalystwhich exhibits excellent efficiencies over a broad temperature range andat high space velocities. More particularly, it is an object to providean oxidation catalyst that exhibits excellent chemical and thermalstability.

Another object of the present invention is to provide an oxidationcatalyst which is effective in selectively oxidizing a broad range ofmolecular species, such as ammonia, carbon monoxide, hydrocarbons, andthe like. More particularly, it is an object to provide an oxidationcatalyst that can be used in the treatment of exhaust gases fromindustrial plants and motorized vehicles utilizing fossil fuels for theremoval of substantially all carbon monoxide, combusted and partiallycombusted hydrocarbons, oxygenated hydrocarbons and oxides of nitrogentherefrom.

Ceramic, stoichiometric compounds of the following empirical formula areknown and have been used in high temperature electrodes:

    X'.sub.n J'.sub.(1-n) Z'O.sub.3,

wherein

X' is Strontium;

J' is Yttrium or Lanthanum,

Z' is a metal of the first transition series, and

n is 0 or 0.22.

W. f. libby has suggested that one of these catalysts (LaCoO₃) might bea promising catalyst for Auto Exhaust. However, he furnished no data tosupport this suggestion [see Science, Vol. 171, pages 499-500 (1971)].

The catalyst of the present invention is a ceramic, mixed oxide,nonstoichiometric electrically neutral catalyst containing arare-earth-type element or mixture thereof, a metal of the firsttransition series or mixtures thereof, Zirconium, Tin or Thorium ormixtures thereof, oxygen atoms, and optionally an alkaline earth metalor mixture thereof. The transition metal or metals are present as mixedoxides wherein the metal is present in more than one oxidation state.The rare-earth-type element or elements can also be present in more thanone oxidation state.

The alkaline earth metals include beryllium, magnesium, calcium,strontium, barium, and radium. In the present invention the preferredalkaline earth elements are magnesium, calcium, strontium, and barium.The rare-earth-type elements are scandium, yttrium and therare-earth-elements, e.g., lanthanum, cerium, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium. In the presentinvention the preferred rare-earth-type elements have atomic numbersbetween 20 and 72. The metals of the first transition series includetitanium, vanadium, chromium, manganese, iron, cobalt, nickel, copperand zinc. In the present invention the preferred metals of the firsttransition series include those metals having an atomic number between21 and 30. At least 0.01% of the transition metal atoms of the oxidecatalyst have oxidation states other than +3; i.e., at least 0.01% ofthe transition metal atoms are present in oxidation states higher orlower than +3. In the preferred embodiment of the present invention, atleast 0.1% of the transition metal atoms in a mixture of metal oxideshave oxidation states other than +3. Although there is no upper limit tothe percentage of metal atoms having oxidation states other than +3,rarely will more than 35% of the transition metal atoms have oxidationstates deviating from +3. The rare-earth-type elements may be present inmore than one oxidation state, i.e., between and including +2 to +4.

The ceramic, mixed oxide, nonstoichiometric, electrically neutralcatalyst of the present invention is a solid crystalline compound at thetemperature at which it is used. Elements represented by W, X, J and Zof formula (I) are present in the catalyst as positively charged ionsand the oxygen is present as negatively charged ions. The chemicalbonding between W, X, J, Z and O is most accurately described as beingionic. As a solid chemical compound the catalyst is partiallycharacterized, we believe, by its crystal structure. It differs from thecrystal structures of catalysts described as mixtures of oxides such asthe hopcalites which are mixtures of metal oxides and not a homogenousmixed oxide compound.

Electrical neutrality in the mixed oxide catalysts of the presentinvention can be understood in terms of classical theory regarding ionicspecies and present theories regarding defect chemistry. Electricalneutrality in the present mixed oxide catalyst, in which fractions ofthe elements represented by Z and J are present as positive ions withcharges other than +3, is maintained by a balance of negatively chargedand positively charged ionic species and the presence of defects such aspositively charged holes, interstitial positive ions, positive ionvacancies, negatively charged electrons and oxygen vacancies. An oxygenvacancy is an empty oxygen lattice site in a crystal structure normallyoccupied by 0⁻² ions. The defects are particularly important inbalancing the X and Z elements having charges other than +3. A fractionof the oxygen vacancy defects may exist as oxygen vacancy defectcomplexes in which the oxygen vacancy is localized preferentially abouta particular positively charged ion. The catalyst exhibits highelectrical conductivity at temperatures at which the defects, i.e.,holes, vacancies, or electrons are mobile. Ionic conductivity within thecatalyst is associated with the mobility of ions such as oxygen ions andis enhanced by the presence of defects such as oxygen vacancies oroxygen vacancy complexes.

It appears that the surprising activity of the present catalyst arisesfrom the nonstoichiometric character of the metal oxide compositioncontained therein. The present catalyst has a very high electronicconductivity and ionic conductivity. The sum of the electronicconductivity and the ionic conductivity is the electrical conductivityof material and is inversely proportional to the electrical resistanceof the material. The present catalyst has an electrical conductivity ofabout 0.1 ohms ⁻¹ cm.⁻¹ to about 1000 ohms ⁻¹ cm.⁻¹. The ionicconductivity is a measurement of the ion flow or migration through andover a material. Most materials found in nature have very low ionicconductivities; however, molten salts and salts dissolved in water havevery high ionic conductivities. The present catalyst has a high ionicconductivity and will readily permit ions to flow or migrate through andacross its surfaces for the distances of 100 angstroms or more. Thepresent ceramic, nonstoichiometric oxidation catalysts also haveexcellent selective adsorption properties. The present catalysts arerelatively good adsorbers of partially oxidized or partially reducedmolecular species such as carbon monoxide, sulfur dioxide, the oxides ofnitrogen, and hydrogen sulfide, and they are relatively poor adsorbersof fully oxidized or reduced materials, such as carbon dioxide ornitrogen gas. The adsorption qualities of the present catalyst alsoappear to arise from its nonstoichiometric nature.

Without intending to limit the invention by the following discussion, itappears that many of the surprising characteristics of the presentcatalyst can be attributed to its high ionic and electronicconductivity, and selective adsorption characteristics. Under presenttheory, an effective catalyst must be a good adsorber of reactants and arelatively poor adsorber of the reaction products thereof. If thecatalyst is a relatively poor adsorber of reactants, the space velocityof the gas stream containing the reactants and the relative gas pathwaylength throughout the catalyst are usually adjusted to give thereactants and catalytic surface the optimum contact conditions. Therelatively high electronic conductivity of the present catalyst due toeither mobile holes or electrons tends to enhance the effective areas ofthe catalyst by reducing the areas of the space charge regions aroundadsorbed molecules which tend to become polarized or ionic. Underpresent theory, it also appears that if the given reaction is a Red-Oxreaction, that is a reaction involving the oxidation of one reactant andthe reduction of the other reactant, the site of reduction and the siteof oxidation on the catalytic material must be relatively close, such asabout 10 A or less, so that electrons and/or molecular ionic speciesresulting from the partial reduction or oxidation of the reactants canmigrate between the two sites to complete the reaction. For example,when the catalyst is to be employed in the oxidation of carbon monoxidewith water vapor to form carbon dioxide and hydrogen gas, the carbonmonoxide molecule will become attached to an oxidation site and becomechemically excited wherein it will readily accept either monoatomicoxygen or ionic oxygen to form carbon dioxide. A water molecule willbecome attached to a reduction site wherein the water molecule will besplit apart to form diatomic hydrogen and monoatomic or ionic oxygen.The former will escape from the catalyst surface while the latter willmigrate over the catalytic surface or through the catalyst as oxygenions to a nearby carbon monoxide oxidation site to combine therewith andform carbon dioxide which will subsequently escape from the surface ofthe catalyst. If the oxidation and reduction sites are more than 10 Aapart, the conventional catalyst generally will not be very effectiveand will exhibit little catalytic activity. In the present catalyst, therespective reaction site can be separated by distances far exceeding 10A; for example, the reaction sites can be separated by distances of 100A or more, because the catalyst has high ionic and electronicconductivity which provides excellent mobility for electrons and atomicand molecular ionic species. Consequently, in the present catalystelectrons or holes can readily flow and migrate from site to site duringa given chemical reaction and likewise oxygen ions can migrate and flowfrom site to site with relative ease.

The present catalysts are prepared by making up an aqueous solution ofthe corresponding water-soluble salts of the rare-earth-type elements,metals of the first transition series, Zirconium, Tin or Thorium, andalkaline earth metals, if the latter are to be included. Typicalwater-soluble salts that are employed include the nitrate and halidesalts of the rare-earth-type elements, the metals of the firsttransition series, Zirconium, Tin and Thorium, and the alkaline earthmetals. After the aqueous solution is thoroughly mixed, the solution isevaporated at either room temperature or at elevated temperatures todryness and the resulting residue is calcined for several hours atelevated temperatures, such as temperatures between 600° C. and 1500° C.If the salts lack oxygen atoms, the salt mixture is calcined in thepresence of oxygen, i.e., air. The resulting ceramic nonstoichiometricoxidation catalyst is a fine powder which may be sintered to varyingdegrees. It can be milled, pressed and sintered to any desired shape.Alternatively, the powdered catalyst can be moistened, molded orextruded into a desired shape, and then sintered or fired.Alternatively, the present catalyst can be prepared from thewater-insoluble salts, such as the sulfates, carbonates, or oxides ofthe rare-earth-type elements, the metals of the first transition series,Zirconium, Tin or Thorium, and the alkaline earth metals. The salts areparticulated and thoroughly mixed in their appropriate molar amounts.The resulting mixture of salts is then calcined as described above toprepare the ceramic oxidation catalyst of the present invention.preferably the calcined material is ground thoroughly and resinteredseveral times to insure a complete solid reaction.

Referring to the above formula (I), the value of (3±m') is affected bythe oxygen pressure during the calcining step as well as the oxygenfugacity and temperature at which the catalyst is used. If the catalyticstarting material is calcined in the absence of oxygen or at low oxygenpartial pressures such as 10 mm Hg, the value of the quantity (3±m) willbe smaller than if the starting catalytic material is calcined at highoxygen pressures such as 700 mm Hg, 3 atmospheres or the like. The valueof m describing a specific formulation of a catalyst depends also on theconditions of its catalytic use. For example, if two catalytic processesinvolve the same temperature but different oxygen fugacities, the valueof m will be higher for the process characterized by the higher oxygenfugacity.

The catalyst of formula (I) and the ceramic-mixed oxide catalyst of thefollowing empirical formulas can be employed in several noveloxygenation processes:

    X.sub.n J.sub.(1-n) ZO.sub.(3±m)                        (II)

    w.sub.k' Y.sub.(1-k') ZO.sub.3                             (III)

wherein W, X, Y, Z, O and m are as defined above and k' is a numberhaving a value of between 0 and about 0.05 and m is a number having avalue of from 0 to about 0.26. For example, these catalysts can beemployed for a preparation of an oxygenated carbon-hydrogen compoundselected from the group consisting of organic hydroxyl compounds,organic carbonyl compounds, organic carboxylic acid compounds andorganic carboxylic anhydride compounds by reacting a carbon-hydrogenorganic compound selected from the group consisting of aromatic organiccompounds, organic olefinic compounds, organic acetylenic compounds,organic epoxide compounds, organic hydroxyl compounds, and organiccarbonyl compounds with a predetermined amount of an oxygenation agentselected from the group consisting of oxygen and water; and passing theresulting mixture over the catalyst of the above formulas at apredetermined elevated temperature.

Such processes include some of the following illustrated processes:

A. benzene + O₂ → phenol + maleic anhydride

B. naphthalene + O₂ → phthalic anhydride

C. o-xylene + O₂ → phthalic anhydride

D. furan + O₂ → maleic anhydride

E. toluene + O₂ → benzaldehyde + benzoic acid

F. anthracene + O₂ → anthroquinone

phenanthrene + O₂ → phenanthroquinone

G. alkanes + O₂ → l-alkanals

H. l-alkanols + O₂ → l-alkanals

I. alkenes + O₂ → epoxyalkanes

J. epoxyalkanes + H₂ O → alkanediols

K. ethylene + H₂ O → 2 - ethanol

L. l-alkynes + H₂ O → 2 - alkanols

M. acetylene + H₂ O → acetone

N. olefins + O₂ → fatty acids and/or ketones

O. dialkyl carbinols + O₂ → dialkyl ketones

P. propylene + O₂ → acrolein

Q. methane + ammonia + O₂ → hydrogen cyanide

R. hydrocarbon + NO → N₂ + CO₂ + H₂ O

S. co + so₂ + h₂ o → h₂ s + co₂

the processes are carried out with an oxygen containing gas, such as airor oxygen gas. The processes are normally carried out in the gaseousstate with the reactants and oxygen being passed through a bed of theabove catalysts in a carrier gas. However, the processes can beconducted in liquid solids systems employing inert solvents and anoxygen containing gas. Process A is conducted at a temperature betweenabout 300° and about 700° C. The production of maleic hydride is favoredwhen excess oxygen is present, whereas the production of phenol isfavored when less than an equal molar amount of oxygen is present.

Process B is normally carried out at a temperature between about 250°and about 600° C., employing naphthalene/air ratios of 1:5 to 1:200.Contact times of between 0.02 and 10 seconds can be used.

Process C is conducted at a temperature between about 300° and about500° C. employing at least one molar equivalent of oxygen for each moleof ortho-xylene; preferably employing 3 or more molar equivalents ofoxygen. In this process minor amounts of maleic anhydride are alsoproduced. Contact times of between 0.1 and 5 seconds can be used inProcesses C and D.

Process D is conducted at a temperature of about 200° and about 450° C.employing a concentration of around 0.1 to 10 mole-percent furan in anair stream. At least one molar equivalent of oxygen is employed for eachmole of furan present.

Process E is conducted at a temperature between about 300° and about600° C., employing at least 0.25 molar equivalents of oxygen for eachmole of toluene; preferably at least 1 mole equivalent of oxygen. Higherprocessed temperatures and/or molar ratios of oxygen favor theproduction of benzoic acid over benzaldehyde.

Process F is conducted at temperatures between about 300° and about 700°C., employing an excess of oxygen. The product is anthraquinone whenanthracene is the reactant and phenanthraquinone when phenanthrene isthe reactant.

Process G is conducted with a molar excess of oxygen at temperaturesbetween about 300° and about 600° C. at elevated pressures of between 1and 25 atmospheres. The temperature and oxygen concentration areadjusted to maximize the production of the alcohol; however, some of thealcohol is further oxidized to the corresponding aldehyde and/or acid.This process is very valuable for the production of formaldehyde andacetaldehyde or mixed aldehydes from methane, ethane, or natural gas.Alkanes having from 1 to 40 carbon atoms can be employed, though usuallythe alkanes employed will have 25 or less carbon atoms.

Process H is conducted at a temperature between about 200° and about400° C., at alkanol concentrations of about 10 mole percent in air.Contact times of between 0.5 and 10 seconds can be used. Some of thealcohol is oxidized to the corresponding carboxylic acid, i.e., alkanoicacid. The alkanol starting material can have 1 or more carbon atoms,preferably 2 or more carbon atoms.

Process I is conducted at a temperature between about 200° and about400° C., employing alkene concentrations of 1-10 mole percent and O₂concentrations of 5-80 mole percent in the presence of N₂, CO₂ or steam.Contact times of between 0.02 and 10 seconds can be used. This processis very valuable for the production of ethylene oxide and propyleneoxide from ethylene and propylene.

Process J is conducted at a temperature between about 200° and about600° C. in the presence of steam. This process can be conducted atatmospheric pressure of one atmosphere or greater. This process providesa convenient method of preparing ethylene glycol and propylene glycolfrom ethylene oxide and propylene oxide.

Process K is conducted at a temperature between about 200° and about500° C. in the presence of steam. This process is conducted at elevatedpressures up to 300 atmospheres or more employing contact times ofbetween 0.5 and 11 seconds. This process provides a valuable method ofproducing ethanol from ethylene.

Processes L and M are conducted at a temperature between about 200° andabout 600° C. in the presence of steam. This process can also beconducted at elevated pressures up to 300 atmospheres or more.

Process N is conducted at a temperature between about 250° and about600° C. with at least on molar equivalent of oxygen for each mole ofolefin; preferably with a great excess of oxygen. When the carbon atomsof the double bond of the olefin are each substituted with a hydrogenatom, the resulting products are fatty acids. When one or more of thecarbon atoms of the double bond are substituted with two alkyl groups,the products are a mixture of the fatty acids and ketones when onecarbon atom is substituted with two alkyl groups or a mixture of ketoneswhen both carbon atoms are so substituted.

Process O is conducted at a temperature between about 200° and about600° C., employing at least 10 mole percent of the dialkyl carbonol(i.e., secondary alcohol) in the oxygen-containing carrier gas. Thisprocess is useful for the production of acetone from 2-propanol ormethyl amyl ketone (i.e., 2-heptanone) from 2-heptyl alcohol (i.e.,2-heptanol).

Process P is conducted at a temperature between about 200° and about500° C. at elevated pressures up to 300 atmospheres.

Process Q is conducted at a temperature between about 700° and about1100° C., employing equal molar amounts of methane and ammonia and threemolar equivalents of oxygen to produce hydrogen cyanide and water. Thisis a very advantageous process for the preparation of hydrogen cyanidefrom inexpensive, commercially available products.

Process R is conducted at a temperature between about 200° and about1000° C., employing excess amounts of hydrocarbons. This process offersa convenient way of eliminating the oxides of nitrogen from combustiongas exhausts of automobile engines, other heat engines employing fossilfuels and chemical processes which form nitrogen oxides as an undesiredproduct.

Process S is conducted at a temperature between about 200° and about800° C. in the presence of steam. This process provides an advantageousmethod of eliminating sulfur dioxide and carbon monoxide from theexhaust gases of engines employing fossil fuels containing sulfur orsulfur-bearing compounds. The combustion of the engine is controlled sothat equal amounts of CO and SO₂ are produced.

As with any catalytic gas phase process, contact time between thereactant and the catalyst can be varied over a wide range such asbetween about 0.01 to about 10 seconds, to maximize production to thedesired product and minimize side product production. The optimumcontact time for a process, employing a particular catalyst, reactants,and reaction temperature, can be determined by conventional methods andexperiments.

For purposes of this invention, "organic hydroxyl compounds" are organiccompounds containing the HO-group, such as phenol, primary alcohols(i.e., 1-alkanols) and secondary alcohols (i.e., 2-alkanols and dialkylcarbonols). For purposes of this invention, "organic carbonyl compounds"include ketones (i.e., alkanones), quinones and aldehydes (i.e.,alkanols). For purposes of this invention "organic carboxylic acidcompounds" include the fatty acids (i.e., alkanoic acids), such asacetic acid, propanoic acid, caprylic acid, decanoic acids and the like.For purposes of this invention, "organic carboxylic anhydride compounds"include maleic anhydride, phthalic anhydride and the like. For purposesof this invention "aromatic organic compounds" include benzene,naphthalene, xylene, toluene, anthracene, phenthrene, and derivativesthereof. For purposes of the present invention "organic olefiniccompounds" include alkenes, such as ethylene, propylene and the higheralkenes. For purposes of the present invention "organic acetyleniccompounds" (i.e., alkynes) include acetylene, and mono- and di-alkylsubstituted acetylene derivatives. Organic epoxide compounds (i.e.,epoxy alkanes) include ethylene oxide, propylene oxide and the like.

The catalysts of the following empirical formula:

    W.sub.K X.sub.n J.sub.(1-k-n) ZO.sub.(3±m)              (IV)

wherein W, X, J, Z, O, k, m and n are as defined above and can beemployed in the oxidation of a wide variety of molecular species. Forexample, the above catalysts can be utilized in the following oxidationreactions:

    ______________________________________                                         U.   2CO + O.sub.2                                                                             ##STR1##                                                     V.   2H.sub.2 + O.sub.2                                                                        ##STR2##                                                    W.                                                                                  ##STR3##                                                                 X.   2SO.sub.2 + O.sub.2                                                                       ##STR4##                                                     Y.   2H.sub.2 S + 3O.sub.2                                                                     ##STR5##                                                     Z.   4NH.sub.3 + 4O.sub.2                                                                      ##STR6##                                                     AA.  4NH.sub.3 + 5O.sub.2                                                                      ##STR7##                                                     BB.  2NO + O.sub.2                                                                             ##STR8##                                                     CC.  2CO + 2NO                                                                                 ##STR9##                                                     DD.  CO + H.sub.2 O                                                                            ##STR10##                                                    EE.  4CO + 2SO.sub.2                                                                           ##STR11##                                                    FF.  4H.sub.2 S + 2SO.sub.2                                                                    ##STR12##                                                   GG.  Hydrocarbons + CO + CO.sub.2 + H.sub.2 O + N.sub.2 + O.sub.2              (slight excess)                                                                            ##STR13##                                                       ______________________________________                                    

Reactions U-BB and GG normally will be carried out with atmosphericoxygen, i.e., with air. In such cases, in each of these oxidationreactions there will be little concomitant oxidation of the atmosphericnitrogen to the nitrogen oxides such as a nitric oxide. However,reactions U-BB and GG can be carried out with any oxygen containing gas.Reaction U can be conducted with only a trace of carbon monoxide andrequires only a slight excess of the stoichiometric amount of oxygenneeded for the complete combustion oxidation of the carbon monoxide tocarbon dioxide. The reactants, i.e., the carbon monoxide and oxygen, arepassed through a bed of the catalyst at a temperature between about 100°C. and about 1000° C. Reaction V can be conducted with only a traceamount of hydrogen and requires only a slight excess of a stoichiometricamount of oxygen needed for the oxidation of the hydrogen. In thisreaction the reactants are passed through a bed of the catalyst at atemperature between about 100° C. and about 500° C. Reaction W can bepracticed with hydrocarbons, such as methane, butane, benzene, or thelike, aldehydes such as acetaldehyde or hexanol, ketones, such asacetone or diacetone alcohol, alcohols, such as methyl alcohol, propylalcohol, or the like, carboxylic acids, such as acetic acid, decanoicacid, or mixtures of the above. This reaction requires an excess of thestoichiometric amount of the oxygen needed for the complete combustionof the above-described reactants. The reactants and oxygen are passedover the catalyst at temperatures between about 100° C. and about 1000°C. At higher temperatures the reaction rate is appreciably increased andpermits very high space velocities. Reaction X can be conducted withtrace amounts of sulfur dioxide and requires an excess of thestoichiometric amount of oxygen needed for the oxidation of the sulfurdioxide. The reaction is conducted through a bed of the catalyst at atemperature between about 120° C. and about 800° C. Reaction Y can beconducted with a trace amount of hydrogen sulfide and requires an excessof the stoichiometric amount of oxygen needed for the oxidation of thehydrogen sulfide. The reaction is conducted by bringing the reactants incontact with the catalyst at a temperature between about 100° C. andabout 700° C. Reaction Z can also be conducted with trace amounts ofammonia and requires an excess of the stoichiometric amount of oxygenneeded for the oxidation of the ammonia. The reaction is carried out bybringing the reactants in contact with the catalyst of the presentinvention at a temperature between about 100° C. and about 400° C.,preferably between about 250° C. and about 400° C. Reaction AA is a veryuseful reaction and provides a method of making nitric oxide, the firststage in the manufacture of nitric acid. The reaction requires only aslight excess of the stoichiometric amount of oxygen needed to oxidizethe ammonia to nitric oxide. The reaction is conducted at temperaturesbetween about 100° C. and about 1000° C., preferably at a temperature ofabout 400° C. or higher. Reaction BB represents the second stage in themanufacture of nitric acid from ammonia. The reaction is conducted attemperatures between about 100° C. and about 400° C. Reaction CC is alsoa very useful reaction and it provides a route for the elimination ofboth carbon monoxide and nitric oxide from the exhaust gas of industrialplants and motorized vehicles utilizing fossil fuels. Both recatants canbe present in trace amounts and can be present in equal stoichiometricamounts. The reaction is carried out in the presence of the catalyst ata temperature between about 200° C. and about 1000° C. When the reactionis conducted in the presence of oxygen or atmospheric oxygen, reactionsU and BB are favored and the principal by-products will be carbondioxide and nitrogen dioxide. Reaction DD is also a useful reaction andprovides an alternative route for the elimination of carbon monoxide inexhaust gases produced by the combustion of fossil fuels. Both reactantscan be present in trace amounts and either can be in excess. Thisreaction is also useful for commercial production of hydrogen. Thereaction is conducted in contact with the catalyst at a temperaturebetween about 150° C. and about 500° C. If this reaction is conducted inthe presence of atmospheric oxygen, reaction U is favored and theprincipal reactants are carbon dioxide and water from the combustion ofhydrogen and atmospheric oxygen. Reactions X and Y provide a means ofinexpensively producing sulfur trioxide for sulfuric acid productionfrom sulfur dioxide and/or hydrogen sulfide. The reactions can beconducted with pure oxygen or with oxygen enriched air. Reaction Zprovides a means of inexpensively producing nitrous oxide. This reactioncan be conducted with pure oxygen or with oxygen enriched air. ReactionGG is a reaction between atmospheric oxygen and an exhaust gas fromindustrial plants or motor vehicles burning fossil fuels with an oxygendeficiency. The exhaust gas will contain hydrocarbons and/or aldehydes,ketones, alcohols, carboxylic acids, and the like, carbon monoxide,carbon dioxide, water vapor, and atmospheric nitrogen. The reaction isconducted with a slight excess of atmospheric oxygen, that is a slightexcess of the stoichiometric amount of oxygen needed for completelycombusting the hydrocarbons or other like organic species and carbonmonoxide to CO₂ and H₂ O. The effluent gas will contain carbon dioxide,water vapor, atmospheric nitrogen and residual oxygen and will besubstantially free of hydrocarbons, carbon monoxide, and oxides ofnitrogen, particularly nitric oxide. The exhaust gases are put incontact with the catalyst of the present invention at a temperaturebetween about 200° C. and about 700° C., preferably about 400° C.

Reactions EE and FF represent useful reactions for recovering SO₂ aselemental sulfur by catalytic oxidation of CO and H₂ S in the absence ofoxygen. Reaction temperature is normally between 100° C. and 800° C. Thelower reaction temperatures are preferred if the sulfer is subsequentlyseparated from the catalyst by vaporization or dissolution.

As described above, the above catalysts of formulas I and III are veryeffective oxidation catalysts for the harmful gaseous pollutants foundin the exhaust gases of industrial plants and motorized vehiclesutilizing fossil fuels. Accordingly, the catalyst can be used to providemethods of eliminating these pollutants from exhaust gases. For example,one method of eliminating or substantially reducing the nitric oxide,carbon monoxide, and hydrocarbon pollutants from the exhaust gasesgenerated by the combustion of fossil fuels, such as natural gas,gasoline, oil stock and/or coal will comprise the following steps:burning the fossil fuel in an oxygen deficiency environment at atemperature between about 1800° C. and about 850° C. to produce anexhaust gas containing carbon dioxide, carbon monoxide, water vapor,unburned or partially burned fossil fuel and atmospheric nitrogen withthe carbon dioxide and carbon monoxide being present in the ratio ofabout 100 to between about 1 and about 11. The combustion of the fossilfuel produces usable heat energy which in turn is employed to producesteam for steam turbines or expand the gases in a reciprocal engine orgas turbine. After the combustion gas has performed its energy function,its temperature will have dropped to between 300° C. and 700° C. Theresulting cooled combustion gas will then be combined with a slightexcess of atmospheric oxygen, i.e., at least a 1% excess of thestoichiometric amount of atmospheric oxygen needed to fully oxidize theremaining uncombusted or partially combusted fossil fuel and carbonmonoxide in the combustion gas. The resulting air combustion gas mixturewill then be passed through a bed of the catalyst at a temperaturebetween about 300° C. and about 700° C. to fully oxidize the carbonmonoxide and fossil fuel. The effluent gas will contain carbon dioxide,water vapor, atmospheric and residual oxygen. The effluent gas will besubstantially free of all fossil fuels or remnants thereof, carbonmonoxide and nitric oxide. When the first combustion step is conductedat 1200° C. and the subsequent catalytic treatment is conducted at 600°C. the resulting effluent gas will contain less than 10 ppm of fossilfuels or remnants thereof, less than 50 ppm of carbon monoxide and lessthan 60 ppm of nitric oxide.

In sharp contrast the present industrial plants, such assteam-generating plants which burn fossil fuel and use a single-stepcombustion process employing excess oxygen, produce an exhaust gascontaining 500 ppm of fossilized fuel or remanants thereof, more than250 ppm of carbon monoxide and more than 340 ppm of nitric oxide. Thesepollutants, as described above, are a major contributor to photochemicalsmog.

The situation in motorized vehicles is even worse. Less than 10% of themotorized vehicles are properly adjusted and have their smog emissiondevices working at optimum conditions. The remainder of the vehicles arenot properly tuned, have inoperative or poorly operating smog emissiondevices and/or faulty mufflers. The motorized vehicles emit vastquantities of unburned or partially combusted gasoline, massive amountsof nitric oxygen and appreciable amounts of carbon monoxide.

The present invention contemplates a method utilizing the above catalystfor operating a motorized vehicle which will emit an exhaust gas whichis substantially free of fossil fuels or remnants thereof, carbonmonoxide and nitric oxide. Preferably the gasoline employed in themotorized vehicle would be lead free. However, gasolines containing lessthan 1 gram of lead per gallon could be utilized in the method describedherein since the catalysts are relatively insensitive to leadcontamination.

The reciprocal engine will be adjusted to run on a rich mixture, thatis, the engine will be run with an overall deficiency of oxygen. Theengine can be adjusted so that it runs on an oxygen deficiency ofbetween 10% and 0.1% so as to limit the formation of nitric oxide. Theexhaust gases from the combustion chambers of the engine are vented orpiped into a catalytic muffler containing the ceramic, mixed oxidecatalyst of the present invention. The exhause gases would containunburned fuel or partially burned fuel, carbon dioxide, carbon monoxide,water vapor, and atmospheric nitrogen. Just before entering thecatalytic muffler, the combustion gases could be combined with at least1% of excess of atmospheric oxygen, that is, at least 1% in excess ofthe stoichiometric amount of oxygen needed for the complete combustionof the carbonaceous material in the combustion gas. The resultingmixture would then be passed through the catalytic muffler at atemperature between about 100° C. and about 700° C. The resultingeffluent gas would contain carbon dioxide, water vapor, atmosphericnitrogen, and residual oxygen. The effluent gas would be substantiallyfree of all fuel and remnants thereof, carbon monoxide, and nitricoxide.

The above catalysts are ideally suited to the above-described method fortwo reasons: (1) the catalysts are relatively unaffected by metallicsubstances, such as lead, and (2) the present catalysts will selectivelyoxidize carbonaceous material, such as carbon monoxide and hydrocarbons,in preference to atmospheric nitrogen over a broad range oftemperatures.

The present catalyst can also be used to produce a two-step catalystprocess for removing gaseous pollutants from fossil fuel exhausts, thatis, the exhaust gases produced by the combustion of fossil fuels. Inthis method, the fossil fuel can be burned with a stoichiometric amountof atmospheric oxygen or a slight deficiency. The fossil fuel can beburned at a temperature of 1000° C. or higher. The fossil fuel is burnedwith a deficiency of oxygen in order that at least as much carbonmonoxide, on a molar basis, is produced as nitric oxide, preferably atleast twice as much carbon monoxide is produced; nitric oxide productionis disproportionately increased at high combustion temperatures. Thecombustion gases will contain fossil fuel, partially combusted fossilfuel, carbon dioxide, carbon monoxide, water vapor, nitric oxide andatmospheric nitrogen. If fossil fuel contains sulfur or sulfurcontaining compounds, sulfur and hydrogen sulfide will also be found inthe combustion gases. After the combustion gases have fulfilled theirenergy function, they will have cooled to about 700° C. or less. Thecooled combustion gases are passed through a bed of the catalyst whereinthe carbon monoxide is oxidized by nitric oxide and water to carbondioxide. If the fuel contains sulfur containing compounds, the resultingeffluent gas may be cooled to recover the sulfur. The resulting effluentgas is then mixed with a slight excess of atmospheric oxygen and passedthrough a second bed of catalyst of the present invention wherein thefossil fuel, partially combusted fossil fuel, remaining carbon monoxide,remaining nitric oxide, hydrogen sulfide, and sulfur are fully oxidizedyielding an exhaust gas consisting essentially of carbon dioxide, watervapor, sulfur trioxide, atmospheric nitrogen, nitrogen dioxide andresidual atmospheric oxygen. The exhaust gases will be essentially freeof the gaseous pollutants, i.e., oxides of nitrogen and sulfur. Thismethod is particularly applicable for use on motorized vehicles and hightemperature industrial plants wherein a large quantity of nitric oxideis produced during the combustion step.

The catalysts of formulas (III) and (IV), wherein m has a value otherthan 0, are prepared in the same manner as the catalyst of formula (I).The catalysts of formulas (I) and (IV), wherein m has a value of 0, canbe prepared by conventional methods, such as the method disclosed by G.H. Zonker, Philips Research Reports, 24, 1-14 (1969). The maximum valueof k and k" in the catalysts of formulas (I), (IV) and (V), infra, isreduced when n and n' in the formulas have values of 0 because thesolubility of Zirconium, Tin and Thorium in the catalyst composition isreduced in the absence of alkaline earth metals in the catalystcomposition. The above catalysts can be formed and utilized in variousstates and shapes, such as powdered form, pellets, flakes, and the like.The catalyst can be sintered to varying degrees. For the industrialplant use or catalytic muffler use, the catalyst can be used as apowder, as pressed sintered pellets, macaroni-shaped tubes, flat orcurved flakes, honeycombed plates, and the like. The catalyst also canbe used on a support such as a ceramic refractory, glass or high-meltingmetal support substance. As mentioned above, the powdered catalyst canbe pressed into shape and fired or sintered to fix the shape.Alternatively, the powder material can be made plastic by mixing withwater or with an organic binder and extruded into any desired shape andsintered or fired into that shape. In another alternative method, thecatalyst can be made into a liquid paint or ink which can be used tocoat a support or walls, such as muffler walls, and the like. After thecoating is complete, the catalytic paint or ink can be dried and firedto fix the coating to the underlying support or wall. If an extremelythin layer, such as 10³ A, of the catalyst on a particular support isrequired, the catalyst can be coated on the support by ionic sputtering.

The operating temperature ranges cited are particularly wide for thecatalyst. This results from the low, high and overlapping temperaturesover which specific examples of the catalyst of the present inventionare characterized by high electronic and ionic conductivities whichcontribute to the electrical conductivity. This desired feature permitsoptimization with regard to chemical and thermal stability for aspecific application.

The following examples are included to further illustrate the presentinvention and are not intended as limitations thereof.

EXAMPLE 1

An aqueous mixture of 49.5 moles of a lanthanum nitrate (La(NO₃)₃), 50.0moles of cobalt nitrate (Co(NO₃)₂) and 0.5 mole of Th(NO₃)₄ is preparedfrom the corresponding lanthanum, cobalt and thorium nitrate salts. Thesolution is boiled and evaporated to dryness; the resulting residue iscalcined in air for 7 hours at 1200° C. to produce a fine powder havingthe following empirical formula:

    Th.sub.0.01 LA.sub.0.99 CoO.sub.3.

a substantially identical catalyst is prepared by employing thecorresponding chloride salts in place of the nitrate salts in the aboveprocedure.

The above powdered catalyst is moistened with distilled water andglycerine to prepare a thick paste which is extruded intomacaroni-shaped tubes. The tubes are air-dried for 48 hours and thenfired at 1300° C. for 3 hours.

EXAMPLE 2

An aqueous solution containing 1 mole of tin chloride, 1 mole of bariumchloride, 8 moles of yttrium chloride and 10 moles of titanium chloridewas prepared by dissolving the corresponding chloride salts in 100liters of water. The resulting aqueous solution was evaporated todryness under a vacuum. The resulting residue was calcined for 10 hoursat 1200° C. under an atmosphere of air to produce a fine powder havingthe following empirical formula:

    Sn.sub.0.1 Ba.sub.0.1 Y.sub.0.8 TiO.sub.3.

the resulting powder was pressed into cylindrical pellets measuring 5millimeters by 2.5 centimeters in a hydraulic press at 10,000 psi andsintered at 1100° C.

EXAMPLE 3

A catalyst is made by the procedure of Example 1 by calcining under aninert argon gas atmosphere to produce a fine ceramic powder having thefollowing empirical formula:

    TH.sub.0.01 La.sub.0.99 CoO.sub.(3-m).

wherein m has a value between 0 and 0.26.

EXAMPLE 4

A catalyst is made by the procedure of Example 1 employing 6 moles ofchromium nitrate in place of cobalt nitrate and calcining under a 100%oxygen gas atmosphere to produce a ceramic powder having the followingempirical formula:

    TH.sub.O.01 La.sub.0.99 CoO.sub.(3+m)

wherein m has a value between 0 and 0.26.

EXAMPLE 5

An aqueous solution containing 1.0 mole of Zirconium chloride, 3 molesof calcium bromide, 6.5 moles of a mixture of cerium nitrate, neodymiumnitrate, and lanthanum nitrate, and 10 moles of nickel chloride areprepared by heating 75 liters of distilled water to boiling and addingthe above corresponding salts of zirconium, calcium, cerium, neodymium,lanthanum and nickel. The solution is boiled to dryness and the residueis calcined under a nitrogen gas atmosphere for 5 hours at 1150° C. toproduce a crusty residue of the empirical formula:

    Zr.sub.0.1 Ca.sub.0.3 (CeNdLa).sub.0.6 NiO.sub.(3-m)

wherein m is a value between 0 and 0.26, which powdered on scraping. Theresulting powder is moistened with water and starch to produce a thinpaste. Neutral alumina pellets are rolled through the paste to coat thecatalyst thereon. The coated pellets are air-dried and fired at 1250° C.for 18 hours to bond the catalyst coating to the pellets.

EXAMPLE 6

A 100 liter aqueous solution containing 0.001 moles of thorium chloride,0.1 mole of calcium chloride, 9.889 moles of a mixture of rare earthnitrates wherein the rare earth elements have atomic numbers from 57 to71, and 10 moles of a 50:50 mixture of chromium and manganese nitrate.The resulting aqueous solution is boiled to dryness at 1 mm. of Hgvacuum and the resulting residue is calcined for 8 hours at 800° C.under an atmosphere of air at 2 atmospheres pressure. The resultingcatalyst powder is pressed into spherical shapes measuring 5 millimetersin diameter and sintered at 1100° C.

EXAMPLE 7

To 1000 liters of water, there are added 1 mole of zirconium nitrate, 28moles of strontium chloride, 70 moles of ytterbium chloride, 1 mole oflutetium chloride, and 100 moles of vanadium chloride. The resultingmixture is heated and stirred to form a solution which is filtered andevaporated to dryness at room temperature under vacuum to form a dryresidue. The residue is calcined to 1050° C. for 8 hours under anatmosphere of air to produce a ceramic powder.

The powder is moistened and pressed into flat sheets 2.5 millimetersthick; the pressed sheets are dried and fired at 1200° C. for 9 hours toform ceramic sheets which are thereafter broken into 1 centimeterflakes.

The other catalysts disclosed herein [the catalyst of formulas (I), (II)and (III)] can be prepared by the processes of the above examples byemploying the appropriate molar amounts of transition metal andrare-earth salts and optionally salts of the alkaline earth metals orZirconium, Thorium or Tin.

EXAMPLE 8

A mixture of 0.2 g. of stannic oxide, 4.3 g. of magnesium acetate, 28.8g. of barium carbonate, 69.0 g. of lanthanum carbonate, 57.4 g. oferbium oxide, and 59.7 g. of ferric oxide is milled into a fine powder.The resulting powder is pressed into rods 0.1 cm. in diameter and firedat 1200° C. under an atmosphere of nitrogen for 15 hours to producecatalytic ceramic rods.

The rods are broken up to form pellets measuring about 1 cm. in length.

EXAMPLE 9

A mixture of 25.4 g. of thorium sulfate (Th(SO₄)₂), 266 g. of lanthanumsulfate (La₂ (SO₄)₃), 50 g. of chromic anhydride, and 77.5 g. of cobaltsulfate (CoSO₄) is milled to a fine powder. The powder is moistened witha 70:3:30 mixture of water, glycerine and gum arabic to form a paint.The catalytic paint is coated on fired alumina plates and allowed toair-dry. The coated plates are then fired in air at 1100° C. for 36hours to produce a ceramic catalytic plate.

EXAMPLE 10

An air stream containing 10 ppm carbon monoxide was heated to 200° C.and passed through a bed of a ceramic, mixed oxide nonstoichiometric,electrically neutral catalyst having the following empirical formula:

    Zr.sub.0.1 Sr.sub.0.51 La.sub.0.39 CoO.sub.(3±m)

wherein m has a value of from 0 to about 0.26. The catalyst bed measured1 centimeter in diameter and 10 centimeters in length and the velocityof the gas was 10 centimeters per second. The effluent gas was cooled toroom temperature and analyzed with gas liquid chromatography using athermal conductivity detection cell and a 30 foot column containingmolecular sieve which showed that the resulting air stream had less than5 parts ppm. of carbon monoxide and no nitric oxide. Substantiallysimilar results will be obtained by employing the other catalystsdescribed above in the temperature ranges where they are characterizedby having significant electrical conductivities.

Substantially the same results are obtained by employing a ceramic,mixed oxide, nonstoichiometric, electrically neutral catalyst of thefollowing formula:

    Zr.sub.0.1 Sr.sub.0.1 La.sub.0.8 CrO.sub.(3±m),

wherein m has a value of from 0 to about 0.26 and heating the air streamto 400° C.

EXAMPLE 11

An air stream containing 5% carbon monoxide and 10% water is passedthrough a bed of sintered pellets of a ceramic catalyst of the presentinvention having the following empirical formula:

    TH.sub.0.00002 Ca.sub.0.1 La.sub.0.9 NiO.sub.(3±m),

wherein m has a value of from 0 to about 0.26. The catalyst bed measures1 centimeter by 15 centimeters and is heated to about 350° C. Thevelocity for the gas stream is 12 centimeters per second. The effluentgas contains less than 10 parts per million (ppm) carbon monoxide andvirtually no nitric oxide.

EXAMPLE 12

An air stream containing 15% sulfur dioxide is passed through a bed ofceramic flakes of a ceramic nonstoichiometric catalyst having thefollowing empirical formula:

    Sn.sub.0.05 Y.sub.0.95 FeO.sub.(3±m),

wherein m has a value of from 0 to about 0.26. The catalyst is preparedaccording to the procedure of Example 7. The catalytic bed measures 1centimeter in diameter and 12 centimeters in length and is heated to250° C. The effluent gas contains sulfur trioxide and is substantiallyfree of sulfur dioxide, and nitric oxide.

Substantially identical results are obtained when the catalyst ismaintained at a temperature between 300° C. and 450° C.

EXAMPLE 13

An air stream containing 4% hydrogen sulfide is passed through a bed ofa powdered ceramic nonstoichiometric catalyst of the following empiricalformula:

    SN.sub.0.001 Sr.sub.0.2 Ca.sub.0.799 CoO.sub.(3±m),

wherein m has a value of from 0 to about 0.26. The catalyst can beprepared according to the procedure of Examples 1, 3, or 4. The gasstream is heated to 400° C. and the velocity of 20 centimeters persecond is maintained through the catalytic chamber which measures 0.8centimeters in diameter by 12.5 centimeters in length. The effluent gascontains sulfur trioxide, some sulfur dioxide, and water and issubstantially free of hydrogen disulfide and nitric oxide.

EXAMPLE 14

An air stream containing 5% ammonia is heated to 900° C. and pressedthrough a bed of a powdered, ceramic, nonstoichiometric catalyst of thefollowing empirical formula:

    Zr.sub.0.00001 (YLaCeNdSm)NiO.sub.(3±m)

wherein m has a value between 0 and 0.26. The catalyst chamber measures10 centimeters in diameter by 1 meter and the velocity of the gas streamis maintained at 7.5 liters per second. The effluent gas stream isessentially free of ammonia and contains nitric oxide (as nitric oxideand nitrogen dioxide) and water as the major by-products. When thisprocess is conducted at a temperature around 275° C., the majorby-products are nitrous oxide and water.

An air stream containing 10% nitric oxide and heated to 225° C. wasutilized in place of the air stream containing ammonia in the abovemethod to yield an effluent gas stream containing less than 0.2% nitricoxide; the major product is nitrogen dioxide and its dimer.

EXAMPLE 15

A gas stream containing equal portions of carbon monoxide and nitricoxide is passed through a catalytic chamber containing a bed of sinteredceramic nonstoichiometric catalytic pellets of the folowing empiricalformula:

    Th.sub.0.1 Mg.sub.0.3 Ho.sub.0.6 TiO.sub.(3-m),

wherein m has a value of from 0 to about 0.26. The gas stream ismaintained at 650° C. and passed through the catalytic chamber at asufficient space velocity to insure that the reactants are in thecatalytic chamber for approximately 1/10 of one second. The effluent gasis substantially free of carbon monoxide and nitric oxide and consistsessentially of carbon dioxide and nitrogen gas.

The above carbon monoxide-nitric oxide gas stream is replaced with anair stream containing 1% carbon monoxide, 500 ppm nitric oxide, and 2%water. The effluent gas stream is substantially free of carbon monoxide,contains less than 30 parts per million nitric oxide and consistsessentially of atmospheric gases and carbon dioxide.

Example 16

The burners of a steam turbine generating plant boiler are operated withnatural gas fuel so that the maximum flame temperature is 1500° C. Thenatural gas is burned in an oxygen deficiency to yield a combustion gascontaining carbon monoxide, atmospheric nitrogen, water vapor, andcarbon dioxide. The combustion gas also contains some nitric oxide andhydrocarbons. The ratio of CO₂ to CO in the gas is adjusted to a ratioof 95:5 by controlling the air supply. The combustion gas, after beingemployed in producing high-pressure steam, is combined with a 1% excessof atmospheric oxygen at a temperature of about 600° C. and passedthrough a catalytic chamber containing the catalyst of Example 4 at aspace velocity sufficient to insure that the combustion gas is incontact with the catalyst for about 0.10 second to yield a stack gaswhich is substantially free of nitric oxide and carbon monoxide andcontains principally carbon dioxide, water and atmospheric nitrogen.When the fuel is burned with a greater oxygen deficiency to yield a CO₂to CO ratio of 90 to 10, an even cleaner stack gas with respect tonitric oxide is obtained.

With increasing temperatures for the initial combustion stage,increasing portions of nitric oxide will be emitted in the combustiongases. The following table shows the parts per million of nitric oxidepresent in the combustion gas at various combustion temperatures for thefirst stage of combustion.

                  TABLE                                                           ______________________________________                                        Combustion    Parts per million of nitric                                     Temperature   oxide in combustion gas                                         ______________________________________                                        1500° C.                                                                             150          ppm                                                1400° C.                                                                             32           ppm                                                1300° C.                                                                             0.9          ppm                                                1200° C.                                                                             0.09         ppm                                                ______________________________________                                    

The above method provides a method for public utilities to produce powerwith fossil fuels and yet emit a stack gas containing a minimal amountof nitric oxide, carbon monoxide, and unburned fuel. At present, mostpublic utility plants producing energy from fossil fuel emit an exhaustgas containing from about 200 to about 1500 ppm of nitric oxide. In manyareas of the country, such as Los Angeles, public utilities are a majorcontributor, up to 10%, of the nitric oxide in the air.

The above method can be employed utilizing natural gas, oil fuel, orcoal with substantially the same results.

EXAMPLE 17

A carburetor and the timing of a reciprocal engine, which burns agasoline containing 0.5 gm of lead/gallon, is adjusted so that theengine, when operating in its normal operating temperature, burns aslightly rich fuel-air mixture having about a 1% oxygen deficiency. Theexhaust or combustion gas from the cylinders of the reciprocal engineare vented through manifolds and exhaust pipes into a mixing chamberwherein the combustion gases are mixed with a slight excess ofatmospheric oxygen, that is a 1% excess of the stoichiometric amount ofoxygen needed to fully burn the carbonaceous material, i.e., unburnedand partially burned gasoline and carbon monoxide, present in thecombustion gases. The resulting mixture is then vented into a catalyticmuffler containing an alumina honeycomb matrix coated with a catalysthaving the following empirical formula:

    Zr.sub.0.1 Sr.sub..1 La.sub..8 CoO.sub.(3±m)

wherein m has a value of from 0 to about 0.26. The catalytic chamber isdesigned such that the exhaust gas will travel through the muffler inabout 0.1 second when the engine is working at its maximum revolutionrate. The combustion gas has a temperature of above 300° C. when itcomes in contact with the catalyst. The resulting effluent gas willcontain less than 500 parts per million of carbon monoxide, and will besubstantially free of gasoline or partially burned gasoline.

EXAMPLE 18

The combustion gases from a steam turbine generating plant burningfossel fuels in a 2.1% oxygen deficiency contains carbon dioxide, carbonmonoxide, sulfur, hydrogen sulfide, nitric oxide, atmospheric nitrogen,water vapor, and unburned or partially burned fossil fuel. Thecombustion gas, which is heated to about 700° C., is passed through acatalytic chamber containing the catalyst of Example 6 at such a ratesuch that the catalyst and all the combustion gas come into contact. Thegaseous pollutants in the resulting effluent gas are substantiallyreduced. In particular, the amount of carbon monoxide and nitric oxidecontained therein are substantially reduced because the nitric oxide andwater vapor have oxidized the carbon monoxide to carbon dioxide. Theresulting effluent gas which has now cooled down to about 100° C. andthe sulfur are collected by electrostatic precipitation. The resultinggas is heated to approximately 250° C. and combined with a 0.7% excessof the stoichiometric amount of oxygen needed to fully oxidize theunburned fuel, partially burned fuel, the sulfur-containing compoundsand the remaining carbon monoxide. The resulting air and effluent gasmixture is passed through a second catalytic chamber containing thecatalyst of Example 17. The second catalytic chamber is designed suchthat the gaseous mixture and the catalysts are in contact forapproximately 0.1 to 0.5 seconds. The resulting effluent gas consistsessentially of carbon dioxide, water vapor, atmospheric nitrogen andresidual oxygen. The effluent gas contains less than 80 parts permillion of nitric oxide, less than 50 parts per million of carbonmonoxide, and is substantially free of nitrogen dioxide and unburned orpartially burned fuel.

EXAMPLE 19

A gas stream containing nitric oxides and hydrocarbons is passed througha catalytic chamber containing a bed of the catalyst of the formuladescribed in Example 20. The gas stream is maintained at a temperaturearound 700° C. and passed through the catalytic chamber at a sufficientspace velocity to insure that the reactants are in contact with thecatalyst for at least .1 second. The exhaust gas from the catalyst bedcontains nitrogen gas and the unreacted hydrocarbons.

EXAMPLE 20

A carrier gas containing between 50% and 0.5% benzene is passed througha bed of a catalyst of the following formula (V) at a temperaturebetween about 325° and 500° C. at a sufficient velocity to insure thecontact time between the catalyst and the carrier gas is about 0.1seconds:

    W.sub.k" X.sub.n' J.sub.(1-k"-n') ZO.sub.(3±m)          (V)

wherein W, X, J, Z, O and m are as defined above, and k" is a numberhaving a value of from 0 to about 0.1; and n' is a number having a valueof from 0 to about 0.51, provided when n' has a value of O, k" has avalue of from 0 to about 0.05. The off-gas from the catalyst bed iscooled to about 0° C. and passed through a mist eliminator to condensethe material in the carrier gas for collection. The collected materialscontains principally maleic anhydride together with lesser amounts ofphenol and benzene. The compounds are separated from each other byconventional techniques.

EXAMPLE 21

An air stream containing about 50% benzene vapor is passed through a bedof a catalyst of the formula of Example 20 at a temperature betweenabout 275° and 700° C., at a sufficient space velocity to insure thatthe air stream and the catalyst have a contact time of about 0.1 second.The off stream from the catalyst bed contains phenol and lesser amountsof benzene and maleic anhydride which are separated by conventionaltechniques. The ratio of phenol to benzene and maleic anhydride isincreased with increasing reaction temperature.

EXAMPLE 22

An air stream containing between about 20% to about 0.5% naphthalene ispassed through a bed of catalyst of the formula in Example 20, at atemperature of between about 270° and 600° C. at a sufficient spacevelocity to insure that the air stream in the catalyst has a contacttime of between about 0.02 and 10 seconds. The off-gas from the catalystbed contains phthalic anhydride and unreacted naphthalene; the twocompounds are separated by conventional separation techniques.

EXAMPLE 23

An air stream containing about 5% ortho-xylene is passed through a bedof catalysts of the formula shown in Example 20, a temperature ofbetween about 320 ° and 500° C. at a sufficient space velocity to insurea contact time between about 0.1 and 5 seconds between the ortho-xyleneand the catalyst. The off-gas contains primarily phthalic anhydride andminor amounts of maleic anhydride and unreacted ortho-xylene which areseparated by conventional techniques.

EXAMPLE 24

An air stream containing about 1% furan is passed through a bed ofcatalyst having the formula described in Example 20, at a temperature ofbetween about 250° and about 400° C., at a space velocity sufficient toinsure contact time between the air stream and the catalyst of betweenabout 0.1 and 5 seconds. The off-gas from the catalyst bed containsprimarily maleic anhydride and smaller amounts of furan, the twocompounds are separated by conventional techniques.

EXAMPLE 25

An air stream containing about 10% toluene is passed through a bed ofcatalyst of the formula described in Example 20, at a temperature ofabout 500° C. at a space velocity sufficient to insure that toluene andthe catalyst have a contact time of at least 0.15 seconds. The off-gasfrom the bed of catalyst contains unreacted toluene, benzaldehyde andbenzoic acid. The production of benzoic acid can be favored byincreasing the process temperature and/or increasing the contact timebetween the catalyst and the toluene and/or increasing the O₂ /tolueneratio. The formation of benzaldehyde can be favored by lowering theprocess temperature and/or decreasing the contact time between thetoluene and the catalyst and/or decreasing the O₂ /toluene ratio.

EXAMPLE 26

An air stream containing about 1% anthracene is passed through thecatalyst having the formula described in Example 20, at a temperature ofabout 500° C. and at a space velocity sufficient to insure that thecontact time between the air stream and the catalyst is at least about 1second. The off-gas from the catalyst bed contains anthraquinone andunreacted anthracene which are separated by conventional techniques. Byemploying phenanthrene in the above process, the off-gas will containphenanthraquinone.

EXAMPLE 27

An air stream containing about 10-mol % methanol is passed through a bedof catalyst having the formula described in Example 20, at a temperatureof between about 250° and 500° C., at a space velocity sufficient toinsure contact time between the air stream and the catalyst of betweenabout 0.5 and 10 seconds. The off-gas contains primarily formaldehydeand a small amount of unreacted methanol which are separated byconventional techniques. By employing the higher alkanols, such asethanol or decanol, the corresponding higher alkanals, such asacetaldehyde and decanal, are produced.

EXAMPLE 28

An air stream containing about 5% natural gas consisting essentially ofmethane, ethane, propane, butane, small amounts of pentane is passedthrough a bed of the catalyst of the formula described in Example 20, ata temperature of between about 350° and 500° C. at a space velocitysufficient to insure a contact time of at least 1 second between the gasstream and the catalyst. The gas stream is pressurized between about 1and 25 atmospheres. The off-gas from the catalyst bed contains thecorresponding aldehydes or alkanals of the hydrocarbons. For example,methanal is produced from methane and ethanol is produced from ethane.

EXAMPLE 29

A carrier gas containing between about 1 and 10 mol % of ethylene andbetween about 5 and 80 mol % oxygen is passed through a bed of acatalyst of the formula described in Example 20, at a temperature ofbetween about 200° and 350° C., at a sufficient space velocity to insurea contact time between the catalyst and the carrier gas of between 0.02and 1 second. The off-gas from the catalyst bed contains ethylene oxideand lesser amounts of ethylene which are separated by conventionaltechniques.

EXAMPLE 30

A carrier gas containing about 1% propylene oxide and 10% steam ispassed through a bed of a catalyst of the formula described in Example20, at a temperature of between about 150° and 250° C., at a sufficientspace velocity to insure contact time between the catalyst and thecarrier gas is at least one second. The off-gas of the catalyst bedcontains propylene glycol (1,2-propanediol) and propylene oxide whichare separated by conventional methods. By employing ethylene oxide inthis process, ethylene glycol is obtained.

EXAMPLE 31

A carrier gas under a pressure up to about 300 atmospheres andcontaining about 10% propylene and about 10% steam is passed through abed of a catalyst of the formula described in Example 20, at atemperature of between about 250° and 450° C., at a sufficient spacevelocity to insure the contact time between the catalyst and the carriergas is between about 1 and 10 seconds. The off-gas from the catalyst bedcontains isopropyl alcohol and propylene which are separated byconventional techniques. By employing ethylene in this process, ethanolis obtained.

EXAMPLE 32

A carrier gas containing about 10% methyl acetylene and 10% steam ispassed through a bed of a catalyst of the formula described in Example20, at a temperature of about 400° C., at a sufficient space velocity toinsure that the contact time between the catalyst and the carrier gasesis at least about 5 seconds. The off-gas from the catalyst bed containsisopropyl alcohol and methyl acetylene which are separated byconventional techniques.

EXAMPLE 33

A carrier gas containing about 1% acetylene and about 10% steam ispassed through a bed of a catalyst of the formula described in Example20, at a temperature of between about 250° and 450° C., under anelevated pressure of between about 1 and 300 atmospheres. The off-gasfrom the catalyst bed contains acetylene and acetone which are separatedby conventional techniques.

EXAMPLE 34

A carrier gas containing about 1% oleic acid is passed through a bed ofa catalyst of the formula described in Example 20, at a temperature ofabout 500° C., at a sufficient space velocity to insure the contact timebetween a catalyst and a carrier gas is about one second. The off-gascontains pelargonic, azelaic and oleic acids which are separated byconventional techniques.

EXAMPLE 35

A carrier gas containing about 5% methyl propyl carbinol is passedthrough a bed of a catalyst of the formula described in Example 20, at atemperature of about 500° C., at a sufficient space velocity to insurethe contact time between the catalyst and the carrier stream is aboutone second. The off-gas contains methyl propyl ketone and methyl propylcarbinol which are separated by conventional techniques.

EXAMPLE 36

An air stream, pressurized between about 1 and 200 atmospheres,containing about 3% propylene, is passed through a catalyst of theformula described in Example 20, at a temperature between about 250° and500° C., and at a sufficient space velocity to insure the contact timebetween the catalyst and the carrier gas is between about 1 and 10seconds. The off-gas from the catalyst bed contains acrolein andpropylene which are separated by conventional techniques.

EXAMPLE 37

An inert carrier steam containing equal molar amounts of methane andammonia, and about 3 molar equivalents of oxygen, is passed through abed of a catalyst of the formula described in Example 20, at atemperature of about 1000° C. The off-gas from the catalyst bed containsunreacted methane ammonia and oxygen together with hydrogen cyanide,carbon monoxide, carbon dioxide and water which are separated byconventional techniques.

EXAMPLE 38

An exhaust gas from the combustion of fossil fuel containing carbonmonoxide and sulfur dioxide in water together with other constituents,such as carbon dioxide, is passed through a catalyst of the formuladescribed in Example 20, at a temperature between about 200° and about800° C., at a sufficient space velocity to insure the contact timebetween the catalyst and the carrier gas of about one second. Theoff-gas from the catalyst bed contains hydrogen sulfide and carbondioxide together with unreacted carbon monoxide or sulfur dioxide,depending on whether carbon monoxide or sulfur dioxide, respectively, isin molar excess in the combustion gas.

EXAMPLE 39

The exhaust gases from a fossil fuel heat enging containing carbonmonoxide and sulfur dioxide are passed through a catalytic chambercontaining a catalyst of the following formula at a temperature of about400° C.:

    zr.sub..05 Be.sub..05 Tb.sub..85 Tm.sub..05 MnO.sub.(3-m)

wherein m has a value of from 0 to about 0.26. The gases are passedthrough the catalyst at a sufficient space velocity to insure that theavailable carbon monoxide reacts with the available sulfur dioxide toyield carbon dioxide, sulfur and the unreacted reactant, if any.

By employing a gas stream containing hydrogen sulfide and sulfur dioxidein the above process, sulfur, water and the unreacted reactant, if any,are obtained.

EXAMPLE 40

The life supporting oxygen containing atmosphere of an enclosed system,as for example in a submarine or space vehicle, is passed through acatalyst chamber containing the catalyst of the following formula heatedto a temperature of about 200° C.:

    sn.sub..05 Gd.sub..95 VO.sub.(3+m)

wherein m has a value of from 0 to about 0.26. Hydrogen present in theatmosphere is oxidized to water to reduce the hydrogen concentration inthe atmosphere to 10 ppm. or less.

I claim:
 1. A process for the oxidation of ammonia to hydrogen cyanidewhich comprises:combining ammonia with a predetermined amount of oxygenand methane to produce hydrogen cyanide and water; and passing theresulting mixture over a ceramic catalyst of the following empiricalformula at a temperature between about 700° and 1100° C.:

    w.sub.k X.sub.n J.sub.(1-k-n)ZO.sub.(3±m')

wherein: W is zirconium, tin or thorium or mixture thereof; X is analkaline earth metal or mixture thereof; J is scandium, yttrium, arare-earth element or mixture thereof; Z is a metal of the firsttransition series or a mixture thereof, at least 0.01 of said metalhaving an oxidation state other than +3; k is a number having a value ofbetween 0 and about 0.1; m' is a number having a value of from 0 toabout 0.26, provided m' has a value other than 0 when n has a value of0; and n is a number having a value from 0 to about 0.51, provided whenn has a value of 0, k has a value of between 0 and about 0.05.